This invention relates generally to Rankine cycle systems and, more particularly, to a method and apparatus for controlling of the flow of a fluid through a vapor generator thereof.
Power generation systems that provide low cost energy with minimum environmental impact, and that can be readily integrated into the existing power grids or rapidly sited as stand alone units, can help solve critical power needs in many areas of the U.S. Gas turbine engines and reciprocating engines are examples of such systems. Reciprocating engines are the most common and most technically mature of these distributing energy sources in the 0.5 to 5 MWe range. These engines can generate electricity at low cost with the efficiencies of 25-40% using commonly available fuels such as gasoline, natural gas, and diesel fuel. However, atmospheric emissions, such as nitrogen oxides (NOx) and particulates can be an issue with reciprocating engines. One way to improve the efficiency of combustion engines without increasing the output of emissions is to apply a bottoming cycle. Bottoming cycles use waste heat from such an engine and convert the thermal energy into electricity. One way to accomplish this is by way of organic Rankine cycle (ORC) power generators, which produce shaft power from lower temperature waste heat sources by using an organic working fluid with a boiling temperature suited to the heat source.
A concern with such use of an ORC is that, if the ORC cycle is interrupted, such as would occur with a failure of a pump, for example, then the refrigerant flow would discontinue and the temperature of the refrigerant within the system would eventually rise to the level of the heat source temperature, which could be well exceed the safe limit of around 350° F. for the refrigerant and cause the refrigerant and/or the lubricant therein to decompose.
Another concern in the design of organic Rankine cycles which use waste heat, is that of corrosion in the boiler. Hot gases from the combustion of natural gases or diesel fuel can be very corrosive if allowed to condense on the heat transfer surfaces of the boiler tubes. Normal practice is to design the boiler such that hot gas exits at 250-350° F., thereby preventing condensation of corrosive exhaust constituents such as sulfuric acid. However, there are times during start up or maintenance when this constraint is not met and condensation and corrosion can occur. Isolation of the boiler from the hot gas stream during these times could prevent condensation, but it is difficult and expensive to produce a high-temperature, low-leakage seal.
In addition to the above needs, there are some circumstances where it is beneficial to be able to divert or reduce the hot gas flow through the boiler. That is, if the exhaust gases being provided to the boiler are substantially in excess of 700° F., which can occur with gas turbine engines, then the refrigerant in the ORC will likely exceed a safe temperature threshold so as to cause decomposition of lubricant in the refrigerant, thereby forming coke which deteriorate boiler performance through excessive boiling and leads to oil loss of the system. Also, the refrigerant itself might decompose when it sees temperatures of excess of 350° F.
It is therefore an object of the present invention to provide an improved boiler heating arrangement for an organic Rankine cycle system.
Another object of the present invention is the provision in an ORC system for preventing excessive refrigerant temperatures in the event of a failure within the ORC system.
Another object of the present invention is the provision in an organic Rankine cycle system for preventing corrosion in a vapor generator/boiler thereof.
Yet another object of the present invention is the provision in the heating portion of an organic Rankine cycle system, for the control of the temperature thereof.
Still another object of the present invention is the provision in an organic Rankine cycle system which is economical to manufacture and effective and efficient in use.
These objects and other features and advantages become readily apparent upon reference to the following description when taken in conjunction with the appended drawings.